Light waveguide data communications (also referred to here as optical data communications) is becoming increasingly popular due to its advantages in relation to systems that use conductive wires for transmission. Such advantages include resistance against radio frequency interference and higher data rates. An example of a light waveguide transmission system is an optical fiber cable link. Such links are widely used for high speed communications between computer systems. Each system that is attached to the link has a transmitter portion and a receiver portion. The transmitter portion includes electronic circuitry that controls a light source such as a laser, to generate a light signal in the cable that is modulated with information and/or data to be transmitted. The light signal is detected at the receiver portion by a light detector, such as a photodiode, and with the help of appropriate circuitry the received data is then demodulated and recovered.
Optical fiber cable causes dispersion in the light signal, making it difficult for the receiver to distinguish between adjacent data symbols in a received sequence. For example, chromatic dispersion penalties in the 1550 nanometer wavelength range are substantial above 10 gigabits/second, thereby limiting the reach of the optical link. To increase the optical reach, a technique known as duo-binary transmission is used which reduces transmission bandwidth relative to that of binary coded transmission, by encoding the transmitted data into three-level (ternary) symbols. Even where the data symbols are encoded using a binary scheme applying a duo-binary code at the receiver has been shown to provide a less drastic decrease in receiver sensitivity that results from chromatic dispersion. Techniques that further improve optical fiber dispersion tolerance at the receiver are still desirable.